The imaging elements to which this invention relates can be of many different types depending on the particular use for which they are intended. Such elements include, for example, photographic, electrophotographic, electrostatographic, photothermographic, migration, electrothermographic, dielectric recording, inkjet ink recording and thermal-dye-transfer imaging elements.
Layers of imaging elements other than the image-forming layer are commonly referred to auxiliary layers. There are many different types of auxiliary layers such as, for example, subbing layers, backing layers, interlayers, overcoat layers, receiving layers, stripping layers, antistatic layers, transparent magnetic layers, and the like.
Support materials for an imaging element often employ auxiliary layers comprising glassy, hydrophobic polymers such as polyacrylates, polymethacrylates, polystyrenes, or cellulose esters, for example. One typical application for such an auxiliary layer is as a backing layer to provide resistance to abrasion, scratching, blocking, and ferrotyping. Such backing layers may be applied directly onto the support material, applied onto a priming or "subbing" layer, or applied as an overcoat for an underlying layer such as an antistatic layer, transparent magnetic layer, or the like. For example, U.S. Pat. No. 4,203,769 describes a vanadium pentoxide-containing antistatic layer that is overcoated with a cellulosic layer applied from an organic solvent. U.S. Pat. Nos. 4,612,279 and 4,735,976 describe organic solvent-applied layers comprising a blend of cellulose nitrate and a copolymer containing acrylic acid or methacrylic acid that serve as overcoats for antistatic layers.
Frequently, when the auxiliary layer serves as the outermost layer, as is the case for a backing layer, it is desirable for this layer to have a low coefficient of friction (COF) to provide proper conveyance properties and to protect the imaging element from mechanical damage during the manufacturing process or customer use. It is known to protect imaging elements against mechanical damage by coating them with a layer comprising a lubricant such as a silicone fluid as described in U.S. Pat. No. 3,489,567, and a wax esters of high fatty acids or high fatty alcohols in U.S. Pat. No. 3,121,060. However, problems are encountered in the use of these lubricants. For example, when silicone is used as a lubricant for a backing layer, it may move to the surface of the support where an image element is to be coated. This will give an adverse effect (e.g. wetting) on the subsequent coating processes. They may also not survive processing so that the advantage of low surface friction is lost for the post-processed products. In addition, it has proven difficult to provide a single layer applied from organic medium that comprises both an abrasion-resistant polymer and a lubricant since it is difficult to find a coating medium that dissolves both the polymer and the lubricant and is at the same time attractive from an enviromental and health standpoint. It is also difficult to form a stable dispersion of a lubricant such as a wax in an organic medium that may be added to a coating composition containing a dissolved, abrasion-resistant polymer. Therefore, in order to form a layer which can be applied from liquid organic medium that is both abrasion-resistant and has a low coefficient of friction one often applies two separate layers; a first layer which is comprised of an abrasion-resistant polymer and then a second layer which is comprised of a lubricant such as a wax. The need to apply these two separate layers increases both manufacturing complexity and cost.
U.S. Pat. No. 4,766,059 describes a method of making solid spherical beads having a mean size ranging form 0.5 to about 20 microns. The polymer beads contain a polymeric resinous material and a water insoluble wax. The process of making such solid beads involves the use of water miscible or immiscible low boiling solvent to dissolve both polymeric materials and wax, and subsequently removal of the solvent or solvent mixture by evaporation. This requires large processing equipment and lengthy processing time, which increases the expenses. U.S. Pat. No. 5,695,919 describes a lubricant impregnated core/shell polymer particle, the polymer particle comprising a core portion which is insoluble in the organic medium and a shell portion which has an affinity for both the core portion and the organic medium.
Therefore, a foremost objective of the present invention is to provide an imaging element with a new lubricant layer composition which survives photographic material processing, does not transfer to the surface of the support to which the imaging layer to be coated, and can be applied from a low hazard organic solvent or solvent mixture.